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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- 将div#demo.demo转化成<div id="demo" class="demo"></div> -->
    <script>
        let str = "div#demo.demo"
        let reg = /^(\w+)\#(\w+)\.(\w+)$/
        var str1 = str.replace(reg,function(match,$1,$2,$3){
            return "<"+$1+" id=\""+$2+"\" class=\""+$3+"\"><\/"+$1+">"
        })
        console.log(str1)

    </script>
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